System for operating internal combustion engine

Abstract

A system for operating an internal combustion engine including an intake valve and an exhaust valve, the system including an exhaust valve gear for the exhaust valve which incorporates an exhaust variable valve timing mechanism. The system also includes an intake valve gear for the intake valve which incorporates an intake variable valve timing mechanism. A control unit operates responsive to a low-speed/low-load operating range of the engine and a low-speed/high-load operating range of the engine to condition the exhaust variable valve timing mechanism for providing advanced opening and closing timings of the exhaust valve to cause a reduced valve overlap between the intake and exhaust valves, and at the same time condition the intake variable valve timing mechanism for decreasing an opening duration of the intake valve to provide a retarded opening timing thereof after a top dead center and an advanced closing timing thereof. The control unit operates responsive to a low-speed/medium-load operating range of the engine to condition the exhaust variable valve timing mechanism for providing retarded opening and closing timings of the exhaust valve to cause an increased valve overlap between the intake and exhaust valves, and at the same time condition the intake variable valve timing mechanism for increasing the opening duration of the intake valve to provide an advanced opening timing thereof before the top dead center and a retarded closing timing thereof.

What is claimed is: 
     
       1. A system for operating an internal combustion engine including an intake valve and an exhaust valve, the system comprising: a crankangle sensor for generating an engine speed signal;   an intake airflow meter for generating an intake airflow rate signal;   an exhaust valve gear for the exhaust valve, said exhaust valve gear incorporating an exhaust variable valve timing mechanism;   an intake valve gear for the intake valve, said intake valve gear incorporating an intake variable valve timing mechanism;   a first hydraulic pressure control valve operatively connected with said intake variable valve timing mechanism;   a second hydraulic pressure control valve operatively connected with said exhaust variable valve timing mechanism; and   a controller electrically connected with said crankangle sensor and said intake airflow meter, said controller being operatively connected with said first and second hydraulic pressure control valves;   said controller being operatively to determine an engine speed data based on said engine speed signal and an intake airflow rate data based on said intake airflow rate signal to determine a fuel amount;   said controller being operatively to determine a low-speed and low-load operating range of the engine when said engine speed data is less than a first reference engine speed, and said fuel amount is less than a first reference fuel amount;   said controller being operatively to determine a low-speed and medium-load operating range of the engine when said engine speed data is less than said first reference engine speed, and said fuel amount is not less than said first reference fuel amount but is less than a second reference fuel amount;   said controller being operatively to determine a low-speed and high-load operating range of the engine when said engine speed data is less than said first reference engine speed, and said fuel amount is not less than said second reference fuel amount;   said controller being operatively to determine a medium-speed operating range of the engine when said engine speed data is not less than said first reference engine speed but is less than a second reference engine speed;   said controller being operatively to determine a high-speed operating range of the engine when said engine speed data is not less than said second reference engine speed;   said controller being operatively responsive to said low-speed and low-load operating range of the engine and said low-speed and high-load operating range of the engine to control said second hydraulic pressure control valve for operating said exhaust variable valve timing mechanism to provide advanced opening and closing timings of the exhaust valve, and at the same time control said first hydraulic pressure control valve for operating said intake variable valve timing mechanism to decrease an opening duration of the intake valve to provide a retarded opening timing thereof and an advanced closing timing thereof to cause a reduced valve overlap between the intake and exhaust valves;   said controller being operatively responsive to said low-speed and medium-load operating range of the engine and said high-speed operating range of the engine to control said second hydraulic pressure control valve for operating said exhaust variable valve timing mechanism to provide a retarded opening timing of the exhaust valve immediately before a bottom dead center of an engine piston stroke and a retarded closing timing thereof, and at the same time control said first hydraulic pressure control valve for operating said intake variable valve timing mechanism to increase the opening duration of the intake valve to provide an advanced opening timing thereof and a retarded closing timing thereof to cause an increased valve overlap between the intake and exhaust valves, a peak of said valve overlap is positioned after a top dead center of the engine piston stroke, said peak of said valve overlap being a point during said valve overlap at which the lift of said intake valve and said exhaust valve is maximum; and   said controller being operatively responsive to said medium-speed operating range of the engine to control said second hydraulic pressure control valve for operating said exhaust variable valve timing mechanism to provide the advanced opening and closing timings of the exhaust valve, and at the same time control said first hydraulic pressure control valve for operating said intake variable valve timing mechanism to cause a medium opening duration of the intake valve between the reduced opening duration and the increased opening duration to cause an intermediate valve overlap between the intake and exhaust valves.   
     
     
       2. A system for operating an internal combustion engine as recited in claim 1, wherein said exhaust variable valve timing mechanism is operatively to move opening and closing timings of the exhaust valve with a predetermined opening duration of the exhaust valve,   said intake variable valve timing mechanism is operatively to alter the opening duration of the intake valve,   said intake variable valve timing mechanism includes a driver shaft having an axis and rotatable about said axis in timed relation with an engine operation, an intake camshaft disposed coaxially with said axis of said driver shaft, and means operatively responsive to operating ranges of the engine to control rotation of said intake camshaft,   said means being operatively responsive to said low-speed and low-load operating range of the engine and said low-speed and high-load operating range of the engine to control said intake camshaft for nonuniform rotation of said intake camshaft relative to said driver shaft to provide said decreased opening duration of the intake valve;   said means being operatively responsive to said low-speed and medium-load operating range of the engine and said high-speed operating range of the engine to control said intake camshaft for uniform rotation of said intake camshaft relative to said driver shaft to provide said increased opening duration of the intake valve.   
     
     
       3. A system as claimed in claim 2, wherein said means includes an annular disk in driving connection with said driver shaft and said intake camshaft, said annular disk having an axis and being shiftable between a first concentric position in which said axis of said annular disk is aligned with said axis of said driver shaft, and a second eccentric position in which said axis of said annular disk is offset from said axis of said driver shaft, and disk driving means for moving said annular disk between said first concentric position and said second eccentric position in response to engine operations, and wherein, when said annular disk is moved to said first concentric position, said intake camshaft is operated to rotate uniformly in speed with said driver shaft, and when said annular disk is moved to said second eccentric position, said intake camshaft is operated to rotate nonuniformly in speed with said driver shaft. 
     
     
       4. A system as claimed in claim 3, wherein said disk driving means is so constructed and arranged as to continuously move said annular disk between said first concentric position and said second eccentric position. 
     
     
       5. A system as claimed in claim 2, wherein said intake camshaft has a cam with a lobe, a peak of said lobe being in contact with the intake valve to provide a maximum valve lift of the intake valve at which no angular phase difference between said intake camshaft and said driver shaft exists. 
     
     
       6. A method for operating an internal combustion engine including an intake valve and an exhaust valve, the method comprising the steps of: generating signals respectively indicative of engine speed and intake airflow rate to obtain an engine speed data and an intake airflow rate data;   determining a fuel amount based on said engine speed data and said intake airflow rate data;   comparing said engine speed data with a reference engine speed;   comparing said fuel amount with a reference fuel amount;   determining an operating range of the engine on the basis of results of the comparison between said engine speed data and said reference engine speed, and the comparison between said fuel amount and said reference fuel amount, said operating range of the engine including a low-speed and low-load operating range, a low-speed and medium-load operating range, a low-speed and high-load operating range, a medium-speed operating range, and a high-speed operating range;   providing, responsive to said low-speed and low-load operating range and said low-speed and high-load operating range, advanced opening and closing timings of the exhaust valve, and at the same time providing, responsive to said low-speed and low-load operating range and said low-speed and high-load operating range, a reduced opening duration of the intake valve to provide a retarded opening timing thereof and an advanced closing timing thereof to cause a reduced valve overlap between the intake and exhaust valves;   providing, responsive to said low-speed and medium-load operating range and said high-speed operating range, a retarded opening timing of the exhaust valve immediately before a bottom dead center of an engine piston stroke and a retarded closing timing thereof, and at the same time providing, responsive to said low-speed and medium-load operating range and said high-speed operating range, an increased opening duration of the intake valve to provide an advanced opening timing thereof and a retarded closing timing thereof to cause an increased valve overlap between the intake and exhaust valves; and   providing, responsive to said medium-speed operating range, the advanced opening and closing timings of the exhaust valve, and at the same time providing, responsive to said medium-speed operating range, a medium opening duration of the intake valve between the reduced opening duration and the increased opening duration to provide a middle opening timing thereof between the retarded opening timing thereof and the advanced opening timing thereof and a middle closing timing thereof between the advanced closing timing thereof and the retarded closing timing thereof to cause an intermediate valve overlap between the intake and exhaust valves.   
     
     
       7. A system for operating an internal combustion engine including an intake valve and an exhaust valve, the system comprising: a crankangle sensor for generating an engine speed signal;   an intake airflow meter for generating an intake airflow rate signal;   an exhaust valve gear for the exhaust valve, said exhaust valve gear incorporating an exhaust variable valve timing mechanism;   an intake valve gear for the intake valve, said intake valve gear incorporating an intake variable valve timing mechanism;   a first hydraulic pressure control valve operatively connected with said intake variable valve timing mechanism;   a second hydraulic pressure control valve operatively connected with said exhaust variable valve timing mechanism; and   a controller electrically connected with said crankangle sensor and said intake airflow meter, said controller being operatively connected with said first and second hydraulic pressure control valves;   said controller being operatively to determine an engine speed data based on said engine speed signal and an intake airflow rate data based on said intake airflow rate signal to determine a fuel amount;   said controller being operatively to determine a low-speed and low-load operating range of the engine when said engine speed data is less than a first reference engine speed, and said fuel amount is less than a first reference fuel amount;   said controller being operatively to determine a low-speed and medium-load operating range of the engine when said engine speed data is less than said first reference engine speed, and said fuel amount is not less than said first reference fuel amount but is less than a second reference fuel amount;   said controller being operatively to determine a low-speed and high-load operating range of the engine when said engine speed data is less than said first reference engine speed, and said fuel amount is not less than said second reference fuel amount;   said controller being operatively to determine a medium-speed operating range of the engine when said engine speed data is not less than said first reference engine speed but is less than a second reference engine speed;   said controller being operatively to determine a high-speed operating range of the engine when said engine speed data is not less than said second reference engine speed;   said controller being operatively responsive to said low-speed and low-load operating range of the engine and said low-speed and high-load operating range of the engine to control said second hydraulic pressure control valve for operating said exhaust variable valve timing mechanism to provide advanced opening and closing timings of the exhaust valve, and at the same time control said first hydraulic pressure control valve for operating said intake variable valve timing mechanism to decrease an opening duration of the intake valve to provide a retarded opening timing thereof and an advanced closing timing thereof to cause a reduced valve overlap between the intake and exhaust valves;   said controller being operatively responsive to said low-speed and medium-load operating range of the engine and said high-speed operating range of the engine to control said second hydraulic pressure control valve for operating said exhaust variable valve timing mechanism to provide a retarded opening timing of the exhaust valve immediately before a bottom dead center of an engine piston stroke and a retarded closing timing thereof, and at the same time control said first hydraulic pressure control valve for operating said intake variable valve timing mechanism to increase the opening duration of the intake valve to provide an advanced opening timing thereof and a retarded closing timing thereof to cause an increased valve overlap between the intake and exhaust valves, a peak of said valve overlap is positioned after a top dead center of the engine piston stroke, said peak of said valve overlap being a point during said valve overlap at which the lift of said intake valve and said exhaust valve is equivalent; and   said controller being operatively responsive to said medium-speed operating range of the engine to control said second hydraulic pressure control valve for operating said exhaust variable valve timing mechanism to provide the advanced opening and closing timings of the exhaust valve, and at the same time control said first hydraulic pressure control valve for operating said intake variable valve timing mechanism to cause a medium opening duration of the intake valve between the reduced opening duration and the increased opening duration to cause an intermediate valve overlap between the intake and exhaust valves.   
     
     
       8. A system for operating an internal combustion engine as recited in claim 7, wherein said exhaust variable valve timing mechanism is operatively to move opening and closing timings of the exhaust valve with a predetermined opening duration of the exhaust valve,   said intake variable valve timing mechanism is operatively to alter the opening duration of the intake valve,   said intake variable valve timing mechanism includes a driver shaft having an axis and rotatable about said axis in timed relation with an engine operation, an intake camshaft disposed coaxially with said axis of said driver shaft, and means operatively responsive to operating ranges of the engine to control rotation of said intake camshaft,   said means being operatively responsive to said low-speed and low-load operating range of the engine and said low-speed and high-load operating range of the engine to control said intake camshaft for nonuniform rotation of said intake camshaft relative to said driver shaft to provide said decreased opening duration of the intake valve;   said means being operatively responsive to said low-speed and medium-load operating range of the engine and said high-speed operating range of the engine to control said intake camshaft for uniform rotation of said intake camshaft relative to said driver shaft to provide said increased opening duration of the intake valve.   
     
     
       9. A system as claimed in claim 8, wherein said means includes an annular disk in driving connection with said driver shaft and said intake camshaft, said annular disk having an axis and being shiftable between a first concentric position in which said axis of said annular disk is aligned with said axis of said driver shaft, and a second eccentric position in which said axis of said annular disk is offset from said axis of said driver shaft, and disk driving means for moving said annular disk between said first concentric position and said second eccentric position in response to engine operations, and wherein, when said annular disk is moved to said first concentric position, said intake camshaft is operated to rotate uniformly in speed with said driver shaft, and when said annular disk is moved to said second eccentric position, said intake camshaft is operated to rotate nonuniformly in speed with said driver shaft. 
     
     
       10. A system as claimed in claim 9, wherein said disk driving means is so constructed and arranged as to continuously move said annular disk between said first concentric position and said second eccentric position. 
     
     
       11. A system as claimed in claim 8, wherein said intake camshaft has a cam with a lobe, a peak of said lobe being in contact with the intake valve to provide a maximum valve lift of the intake valve at which no angular phase difference between said intake camshaft and said driver shaft exists.